المؤلفون: Xu, Chuan-Xiu¹ (AUTHOR) xuchuanxiu715@163.com, Zheng, Guang-Ying^1,2 (AUTHOR)

المصدر: Chinese Physics B. Sep2022, Vol. 31 Issue 9, p1-8. 8p.

مصطلحات موضوعية: *ACOUSTIC wave propagation, *UNDERWATER acoustics, *SPEED of sound, *GROUP velocity, *ACOUSTIC field, *MISSING data (Statistics)

مستخلص: Models based on a parabolic equation (PE) can accurately predict sound propagation problems in range-dependent ocean waveguides. Consequently, this method has developed rapidly in recent years. Compared with normal mode theory, PE focuses on numerical calculation, which is difficult to use in the mode domain analysis of sound propagation, such as the calculation of mode phase velocity and group velocity. To broaden the capability of PE models in analyzing the underwater sound field, a wave mode calculation method based on PE is proposed in this study. Step-split PadĂ© PE recursive matrix equations are combined to obtain a propagation matrix. Then, the eigenvalue decomposition technique is applied to the matrix to extract sound mode eigenvalues and eigenfunctions. Numerical experiments on some typical waveguides are performed to test the accuracy and flexibility of the new method. Discussions on different orders of PadĂ© approximant demonstrate angle limitations in PE and the missing root problem is also discussed to prove the advantage of the new method. The PE mode method can be expanded in the future to solve smooth wave modes in ocean waveguides, including fluctuating boundaries and sound speed profiles. [ABSTRACT FROM AUTHOR]

المؤلفون: Chen, Jin¹ (AUTHOR), He, Xudong¹ (AUTHOR), Chen, Mingji¹ (AUTHOR) mjchen81@bit.edu.cn, Liu, Yongquan² (AUTHOR)

المصدر: Journal of Physics D: Applied Physics. 8/17/2022, Vol. 55 Issue 33, p1-7. 7p.

مصطلحات موضوعية: *FLEXURAL vibrations (Mechanics), *ELECTROMAGNETIC wave propagation, *ELASTIC waves, *REFRACTIVE index, *MAXWELL equations, *ENERGY harvesting, *ACHROMATISM, *LENSES

مستخلص: Conformal transformation method (CTM) has been extensively applied to control propagation of electromagnetic waves and acoustics waves due to the form-invariant property of Maxwell equations and acoustic equations. However, CTM’s application in elastic waves is rarely reported due to the governing equation of elastic waves do not have form invariant property. In this paper, through igniting evanescent waves at the interface of conformally mapped Mikaelian lens with hyperbolic secant refractive index profile, CTM is successfully used to achieve highly efficient (above 75%) broadband (30âˆ'80 kHz) achromatic high-resolution flexural wave focusing in thin plate with full width at half maximum (FWHM) around 0.2 λ. The proposed Mikaelian lens is designed by linking refractive index with the thickness in plates. Simulated results agree well with theoretical prediction. This high performance for flexural wave focusing could be used for energy harvesting and medical imaging. [ABSTRACT FROM AUTHOR]

المؤلفون: Mo, Ya-Xiao¹ (AUTHOR) moyaxiao@mail.ioa.ac.cn, Zhang, Chao-Jin² (AUTHOR), Lu, Li-Cheng¹ (AUTHOR), Guo, Sheng-Ming¹ (AUTHOR)

المصدر: Chinese Physics B. Aug2022, Vol. 31 Issue 8, p1-10. 10p.

مصطلحات موضوعية: *ACOUSTIC wave propagation, *THREE-dimensional modeling, *ACOUSTIC field, *TOPOGRAPHY, *OCEAN, *COUPLED mode theory (Wave-motion)

مستخلص: Large-scale topography, such as a seamount, substantially impacts low-frequency sound propagation in an ocean waveguide, limiting the application of low-frequency acoustic detecting techniques. A three-dimensional (3D) coupled-mode model is developed to calculate the acoustic field in an ocean waveguide with seamount topography and analyze the 3D effect. In this model, a correction is introduced in the bottom boundary, theoretically making the acoustic field satisfy the energy conservation. Furthermore, a large azimuth angle calculation range is obtained by using the operator theory and higher-order PadĂ© approximation. Additionally, the model has advantages related to the coupling mode and parabolic equation theory. The couplings corresponding to the effects of range-dependent environment are fully considered, and the numerical implementation is kept feasible. After verifying the accuracy and reliability of the model, low-frequency sound propagation characteristics in the seamount environment are analyzed. The results indicate lateral variability in bathymetry can lead to out-of-plane effects such as the horizontal refraction phenomenon, while the coupling effect tends to restore the abnormal sound field and produces acoustic field diffraction behind the seamount. This model effectively considers the effects of the horizontal refraction and coupling, which are proportional to the scale of the seamount. [ABSTRACT FROM AUTHOR]

المؤلفون: Stejko, Andrey M.¹ (AUTHOR) ams226@njit.edu, Kosovichev, Alexander G.¹ (AUTHOR), Featherstone, Nicholas A.² (AUTHOR), Guerrero, Gustavo^1,3 (AUTHOR), Hindman, Bradley W.^4,5 (AUTHOR), Matilsky, Loren I.^4,5 (AUTHOR), Warnecke, Jörn⁶ (AUTHOR)

المصدر: Astrophysical Journal. 7/20/2022, Vol. 934 Issue 2, p1-11. 11p.

مصطلحات موضوعية: *ACOUSTIC wave propagation, *HELIOSEISMOLOGY, *ACOUSTIC models, *STANDARD deviations, *MICROSEISMS, *MAGNETOHYDRODYNAMICS

مستخلص: Global hydrodynamic simulations of internal solar dynamics have focused on replicating the conditions for solar-like (equator rotating faster than the poles) differential rotation and meridional circulation using the results of helioseismic inversions as a constraint. Inferences of meridional circulation, however, have provided controversial results showing the possibility of one, two, or multiple cells along the radius. To help address this controversy and develop a more robust understanding of global flow regimes in the solar interior, we apply a “forward-modeling” approach to the analysis of helioseismic signatures of meridional circulation profiles obtained from numerical simulations. We employ the global acoustic modeling code GALE to simulate the propagation of acoustic waves through regimes of mean mass-flows generated by global hydrodynamic and magnetohydrodynamic models: EULAG, the Pencil code, and the Rayleigh code. These models are used to create synthetic Dopplergram data products, used as inputs for local timeâ€"distance helioseismology techniques. Helioseismic travel-time signals from solutions obtained through global numerical simulations are compared directly with inferences from solar observations, in order to set additional constraints on global model parameters in a direct way. We show that even though these models are able to replicate solar-like differential rotation, the resulting rotationally constrained convection develops a multicell global meridional circulation profile that is measurably inconsistent with local timeâ€"distance inferences of solar observations. However, we find that the development of rotationally unconstrained convection close to the model surface is able to maintain solar-like differential rotation, while having a significant impact on the helioseismic travel-time signal, replicating solar observations within one standard deviation of the error due to noise. [ABSTRACT FROM AUTHOR]

المؤلفون: Korobko, Dmitry A¹ (AUTHOR) korobkotam@rambler.ru, Zolotovskii, Igor O^1,2 (AUTHOR), Moiseev, Sergey G^1,2,3 (AUTHOR), Kadochkin, Alexey S^1,2 (AUTHOR), Svetukhin, Vyacheslav V⁴ (AUTHOR)

المصدر: Journal of Optics. Jan2022, Vol. 24 Issue 1, p1-8. 8p.

مصطلحات موضوعية: *ELECTROMAGNETIC wave propagation, *SUBMILLIMETER waves, *POLARITONS, *SCHRODINGER equation, *SURFACE plasmons, *PULSE generators, *METALLIC films, *NONLINEAR waves

مستخلص: Propagation of high-intensity electromagnetic waves in a waveguide structure could initiate nonlinear effects resulting in drastic changes of their spatial and temporal characteristics. We study the modulation instability effect induced by propagation of surface plasmon polaritons in a silver thin-film waveguide. The nonlinear Schrodinger equation for propagating surface plasmon wave is obtained. It is shown numerically that the modulation instability effect can give rise to ultrafast spatial redistribution and longitudinal localization of surface plasmon-polariton wave energy in subwavelength scale. The dependence of plasmon wave dispersion and nonlinear characteristics on metal film thickness is considered. We demonstrate that the use of films with the thickness varying along the waveguide length allows reduction of the generated pulse width and increase of frequency comb bandwidth. The proposed technique is promising for design of ultra-compact (tens of nm) optical generators delivering pulse trains with the repetition rate higher than 1 THz. [ABSTRACT FROM AUTHOR]

المؤلفون: Ouyang, Wen-Chong¹ (AUTHOR), Liu, Qi¹ (AUTHOR), Jin, Tao¹ (AUTHOR), Wu, Zheng-Wei¹ (AUTHOR) wuzw@ustc.edu.cn

المصدر: Chinese Physics B. Sep2021, Vol. 30 Issue 9, p1-9. 9p.

مصطلحات موضوعية: *ELECTROMAGNETIC wave propagation, *ELECTROMAGNETIC wave absorption, *ARGON plasmas, *GLOW discharges, *ARGON, *ELECTRIC discharges, *RADIO frequency, *HELIUM plasmas

مستخلص: A one-dimensional self-consistent calculation model of capacitively coupled plasma (CCP) discharge and electromagnetic wave propagation is developed to solve the plasma characteristics and electromagnetic wave transmission attenuation. Numerical simulation results show that the peak electron number density of argon is about 12 times higher than that of helium, and that the electron number density increases with the augment of pressure, radio frequency (RF) power, and RF frequency. However, the electron number density first increases and then decreases as the discharge gap increases. The transmission attenuation of electromagnetic wave in argon discharge plasma is 8.5-dB higher than that of helium. At the same time, the transmission attenuation increases with the augment of the RF power and RF frequency, but it does not increase or decrease monotonically with the increase of gas pressure and discharge gap. The electromagnetic wave absorption frequency band of the argon discharge plasma under the optimal parameters in this paper can reach the Ku band. It is concluded that the argon CCP discharge under the optimal discharge parameters has great potential applications in plasma stealth. [ABSTRACT FROM AUTHOR]

المؤلفون: Loran, Farhang (AUTHOR) loran@iut.ac.ir, Mostafazadeh, Ali (AUTHOR) amostafazadeh@ku.edu.tr

المصدر: Journal of Physics A: Mathematical & Theoretical. 8/6/2021, Vol. 54 Issue 31, p1-16. 16p.

مصطلحات موضوعية: *ELECTROMAGNETIC wave propagation, *HELMHOLTZ equation, *SCATTERING (Mathematics), *QUANTUM scattering, *TRANSFER matrix, *ABSORPTION coefficients, *SCHRODINGER equation, *SCATTERING (Physics)

مستخلص: The Helmholtz equation in one dimension, which describes the propagation of electromagnetic waves in effectively one-dimensional systems, is equivalent to the time-independent Schrödinger equation. The fact that the potential term entering the latter is energy-dependent obstructs the application of the results on low-energy quantum scattering in the study of the low-frequency waves satisfying the Helmholtz equation. We use a recently developed dynamical formulation of stationary scattering to offer a comprehensive treatment of the low-frequency scattering of these waves for a general finite-range scatterer. In particular, we give explicit formulas for the coefficients of the low-frequency series expansion of the transfer matrix of the system which in turn allow for determining the low-frequency expansions of its reflection, transmission, and absorption coefficients. Our general results reveal a number of interesting physical aspects of low-frequency scattering particularly in relation to permittivity profiles having balanced gain and loss. [ABSTRACT FROM AUTHOR]

المؤلفون: Lanznaster, D L (AUTHOR), de Castro, P B (AUTHOR), Jr, H Emmendoerfer (AUTHOR), Mendonça, P T R (AUTHOR), Silva, E C N (AUTHOR), Fancello, E A (AUTHOR) eduardo.fancello@ufsc.br

المصدر: Inverse Problems. Feb2021, Vol. 37 Issue 2, p1-25. 25p.

مصطلحات موضوعية: *REACTION-diffusion equations, *ACOUSTIC wave propagation, *HAMILTON-Jacobi equations, *ELASTIC wave propagation, *INVERSE problems, *THEORY of wave motion, *FINITE element method

مستخلص: In this work, a topology optimization procedure based on the level-set method is applied to the solution of inverse problems for acoustic wave propagation in the time-domain. In this class of inverse problems the presence of obstacles in a background medium must be identified. Obstacles and background are defined by means of a level-set function that evolves by following the solution of a reaction–diffusion equation. Within this approach, no initial guess for the topology nor level-set reinitialization procedures are necessary, contrary to what is commonly observed when the Hamilton–Jacobi equation is used. The objective function is defined as the domain and time integration of the squared difference between experimental and simulation pressure signals. The finite element method is used for the spatial and level-set function discretizations and a time-marching procedure (Newmark scheme) is used to solve the wave propagation problem, as well as the adjoint problem for the sensitivity analysis. Both procedures provide the information needed to define the velocity field for the level set evolution. Results show that the proposed technique is capable to find the location and shape of obstacles within a background medium. Systematic tests show that, as expected, the distribution of sources and receivers shows to have a major influence on the final solution. Results also reproduce known difficulties; when the so called inverse crime is avoided, the identification procedure worsens its performance. Filters and smoothing are among different features that deserve further investigation. Although the formulation presented here focuses on the acoustic wave propagation problem, its extension to wave propagation in elastic media is straightforward. [ABSTRACT FROM AUTHOR]

المؤلفون: Zhang, Yanqiu¹ (AUTHOR), Zhang, Hao² (AUTHOR), Sun, Tianyu¹ (AUTHOR), Pan, Ting¹ (AUTHOR), Wang, Peiguo³ (AUTHOR), Jian, Xiqi¹ (AUTHOR) jianxiqi@tmu.edu.cn

المصدر: Chinese Physics B. Jul2021, Vol. 30 Issue 7, p1-10. 10p.

مصطلحات موضوعية: *HIGH-intensity focused ultrasound, *ACOUSTIC wave propagation, *TRANSDUCERS, *NONLINEAR wave equations, *COMPUTER simulation, *SOUND pressure

مستخلص: The hemispherical phased transducer maximizes the coverage of the skull and the ultrasonic energy per unit area of the skull is minimized, thereby reducing the risk of skull burns, but the transducer has a small focal area adjustment range, increasing the focal length of treatment is an urgent question for this type of transducer. In this paper, a three-dimensional high-intensity focused ultrasound (HIFU) transcranial propagation model is established based on the human head structure. The finite difference time domain (FDTD) is combined with the Westervelt acoustic wave nonlinear propagation equation and Penne's biological heat conduction equation for numerical simulation of the sound pressure field and temperature field. Forming a treatable focal area in a small-opening hemispherical transducer with a small amount of numerical simulation calculation focusing at a set position to determine the minimum partial excitation area ratio of focusing. And then, applying these preliminary results to a large-opening diameter hemispherical transducer and the temperature field formed by it or full excitation is studied. The results show that the focus area with the excitation area ratio of less than 22% moves forward to the transducer side when the excitation sound is formed. When the excitation area ratio is greater than or equal to 23%, it focuses at the set position. In the case of partial incentives, using 23% of the partial array, the adjustable range of the treatable focal area formed in the three-dimensional space is larger than that of the full excitation. [ABSTRACT FROM AUTHOR]

المؤلفون: Zhang, Fan (AUTHOR) fan.zhang@kuleuven.be, Poedts, Stefaan (AUTHOR), Lani, Andrea (AUTHOR), Kuźma, Błażej (AUTHOR), Murawski, Kris (AUTHOR)

المصدر: Astrophysical Journal. 4/20/2021, Vol. 911 Issue 2, p1-18. 18p.

مصطلحات موضوعية: *ACOUSTIC wave propagation, *ACOUSTIC models, *HYDROSTATIC equilibrium, *CHEMICAL equilibrium, *SHOCK waves, *SOUND waves

مستخلص: To study acoustic wave propagation and the corresponding energy deposition in partially ionized plasmas, we use a two-fluid computational model that treats neutrals and charged particles (electrons and ions) as two separate fluids. This two-fluid model takes into account the ion–neutral collisions, ionization, and recombination, allowing us to investigate both the collisional and reactive interactions between uncoupled ions and neutrals in the plasmas. In the present numerical simulations, the initial density is specified to reach hydrostatic equilibrium, and as a comparison, chemical equilibrium is also taken into account to provide a density profile that differs from typical hydrostatic equilibrium profiles. External velocity drivers are then imposed to generate monochromatic acoustic waves. As is well known, the upward propagating acoustic waves steepen in gravitationally stratified plasmas due to the exponentially decreasing density, and they heat the plasmas in the nonlinear regimes where kinetic energy is dissipated by shock waves and collisional interactions. In particular, the lower ionization fraction resulting from the present initial chemical equilibrium significantly enhances the heating efficiency. Moreover, the ionization process absorbs a significant amount of energy, and the decoupling between ions and neutrals is also enhanced while considering ionization and recombination. Therefore, simulations without considering ionization and recombination may overestimate the overall heating effects but also underestimate the energy dissipation. The results also suggest that a more accurate ionization and recombination model could be essential for improving the modeling of partially ionized plasmas. [ABSTRACT FROM AUTHOR]